Edward Snowden's choice of Hong Kong as a haven from where to leak intelligence documents and to unmask himself as a whistleblower rests on calculations on the territory's press freedom safeguards and its extradition treaty with the US. It is a high-stakes gamble.

Just before sovereignty over Hong Kong passed from Britain to China in 1997, the US signed a new extradition treaty with the semi-autonomous territory. Under that treaty, both parties agree to hand over fugitives from each other's criminal justice systems, but either side has the right of refusal in the case of political offences.

Beijing, which gave its consent for Hong Kong to sign the agreement, also has a right of veto if it believes the surrender of a fugitive would harm the "defence, foreign affairs or essential public interest or policy'' of the People's Republic of China. In short, the treaty makes Snowden's fate a matter of political expediency not just in Hong Kong but in Beijing.

In his Guardian interview, Snowden denied that his decision to fly to Hong Kong to make his allegations on NSA intrusion and infringement of American civil liberties was intended as a vote of confidence in Chinese human rights. But he noted that the people of Hong Kong have "a spirited commitment to free speech and the right of political dissent".

Certainly in comparison with mainland China, Hong Kong is an island of press freedom and political tolerance. When the UK ended 156 years of colonial rule and Hong Kong became China's first 'special administrative region', it was given special status under the principle of "one country, two systems". Most importantly, Hong Kong has its own constitution, its Basic Law, giving it a "high degree of autonomy" on all issues except foreign relations and defence.

The territory has multi-party politics but its chief executive is chosen by an election committee of just a few hundred electors. The freedom of the Hong Kong press, meanwhile, is being continually put to the test. When the government attempted in 2003 to impose restrictions on the grounds of sedition and national security, half a million people came out to demonstrate and the bill was withdrawn.

The tradition of commemorating the 1989 killing of Tiananmen Square demonstrators – banned in the rest of China – is vigorously upheld in Hong Kong. Attendance at a memorial ceremony in the territory's Victoria Park last week was estimated at between 54,000 and 150,000, despite torrential rain.

The combination of a comparatively liberal civic culture and the sovereignty of Beijing, America's great Pacific rival with which it has an often testy relationship, seems to have been a factor in Snowden's choice of Hong Kong. It may play to his advantage that Presidents Barack Obama and Xi Jinping reportedly agreed to differ on cybersecurity issues in their weekend summit in California. Against this background, Snowden's extradition might be seen in the party leadership in Beijing as a capitulation. But such calculations can change.

"Call me naive but I think this is going to come down to how Beijing wants to play this," Josh Marshall argued on his Talking Points Memo blog. "If they don't want a fight over this, Snowden's toast. If they like the optics of it, I don't think it matters what that extradition treaty says. China's a big enough player and the US has enough other fish to fry with the Chinese, that the US is not going to put the bilateral relationship on the line over this guy."

• This article was amended on 28 June 2013 to amend a reference to Hong Kong passing its own Basic Law.